<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script>
    var a = 1000;
  (function(window){
    // console.log(this === window);
    //   console.log(window);
      var a = 100;
  })(window);
</script>
</html>